How much power might a DVD player draw on charge?

[Alison01326]

Hi all

I know nothing about matters electrical (well, nothing worth sharing) and although I have read on here that DVD players are fairly power hungry, do they draw less when being charged?

I normally charge my electrical things up en route, or via the mains if we are on hookup but this weekend we will not be on hookup or driving anywhere (other than home!!). Our portable DVD player should play for 6 hours fully charged but having seen the weather forecast, I have a funny feeling that we're going to be watching it for more than that.

I shouldn't really worry as I have a leisure battery but it would just be interesting to know whether items being charged draw less than they would if they were being used (may need to recharge the torches too).

I look forward to your replies. Thanks.

[Romney_YW]

Whew - simple question, but not so easy answer. It depends on all sorts of things ...

If the player is operating, any current taken to charge it will (obviously) be in addition to the normal operating current, so overall it will be consuming more. But if you can charge the battery with the DVD switched off, the current drawn will be entirely dependant on the design of the charging circuit.

Some chargers charge at a constant current, while others charge to a particular voltage, which roughly means that the current gradually reduces as the battery charge builds up, shutting down to a trickle charge once the battery is full. Some intelligent charges do all sorts of clever things designed to keep the battery in tip-top condition. You might get some idea of the charging current by reading the label on your charger. This will give you the maximum current which it can provide - in practice "normal" charging current would be something less than the maximum.

Once apon a time, the recommended charging current was at the "10-hour rate" - which I think roughly means that it would take 10 hours to fully recharge the batteries. If the DVD player were to flatten the fully-charged batteries in say 5 hours, it would be a reasonable rule-of-thumb to guess that the charging current was half the operating current.

Modern fast chargers though will charge at a much higher current than the 10-hour rate, so again it's difficult to say .... But you might be able to use the same principle here. If your DVD player runs for 6 hours on a fully-charged battery, measure how long it then takes to fully recharge the battery (with the player switched off) - and that should give an idea of the difference between operating and charging current.

I guess I would expect that "normally" something would take longer to recharge than it takes to flatten the charged battery, suggesting that the charging current is lower than the operating current. BUT with some fast chargers, batteries can be recharged very quickly - which must be at a higher current.

Just to add to the confusion, the various currents depend very much on the type of battery being used. Lead acid batteries (like your starter and leisure batteries) need a certain current to charge them to a particular voltage. Older electrical appliances tend to use NiCd batteries, but these have pretty much been replaced by NiMH, Lithium ion or LiPoly - all of which require different conditions to charge them correctly. Also batteries get tired as they get older; a tired battery is more difficult to charge, a lower current passes (less charge goes in) and it goes flat more quickly.

If it helps, you can roughly think of the battery like a bucket of water. You can 'charge' it through a small hose (low current) or a large hose (high current) - and the time it takes to fill depends entirely on the flow rate through the hose. Usually you can pour the water out of the bucket quite quickly, and it then takes a long time to refill. However, if you're pouring the bucket carefully into a funnel (say), it can take quite a long time to empty, and refilling can be much quicker .....

If all else fails, have a look in the manual - it might just tell you the typical values for the current when charging the battery or watching a DVD. On the other hand, it might not

In the end I think, the only sure way to find out (assuming it is actually possible to do) is to connect an ammeter in series between the charger and the player and measure what current is being drawn under each set of circumstances. Can you run the player from the charger? Without batteries installed

And finally, your leisure battery is probably rated at about 100Ah - which is a simple product of the current and time taken. If your DVD player draws 1A, it will flatten your leisure battery roughly in 100 hours. It works both ways - if you then recharge the leisure battery at 2A, it will take roughly 50 hours to fully recharge. (It's actually quite a lot more complicated than this - of course - but that's roughly how it works.) Likewise with the player's own battery. If you know what the Ah rating is and you know it takes 6 hours to flatten, you can roughly guess what the current is. If you know how long it takes to recharge the battery, you can again work out what the current must be.

I'm not sure I've really been of much help here - you're probably now more confused than you were to start with. Battery technology is a very complex subject, and I've probably been guilty of some quite drastic simplification.

And it was such a simple question

PS: It sounds like you're going to be at home - so why not run a mains lead out of the kitchen window and pretend you're on a hook-up?

[welsh winger]

Hi Romney_YW

Well written that man, you covered all sides of the subject in a way a lay man can understand, being an electrician myself I know how complicated this subject can be.

May I suggest this answer is placed where it can be accessed when a similar question arises.

the time it took Romney_YW to think and type out should not be wasted.

Nick
Welsh Winger

[haydn callow]

do they draw less when being charged?
The simple answer to the actual question is NO.

However, I think the answer above covers what you actually ment.

Think of your battery as a tank of water.
Your DVD will draw out of the tank "say" a gallon of water each hour to make it work.

Your charger will refill the tank at a rate of half a gallon per hour.

So your tank of water will last twice as long as if it was not being refilled (charged)

Simples !!

[Alison01326]

Wow, thank you for your fabulously comprehensive reply Romney_YW. And thank you too, Haydn for your response. I will get my calculator out and my husband on standby to do some sums when I get back, as I do not have time now (should have thought of this earlier!!)

Last things first, we are going away!! Poor phrasing on my part as it was late at night. What I meant was that once we arrive at the campsite, the Bongo will not be going anywhere until I drive it home again (ie not driving around over the weekend, so battery will not get a top up). I wish camping outside the house was an option sometimes

As for the DVD player, I've trawled through the specs and it doesn't give a lot of information but I can say this ..

Normally, if we charge the DVD player with the 12v charger, it's a top up charge while we are driving and it "switches off" so to speak when fully charged so I have no idea how long it takes because it has always finished when we stop. The instruction book says it takes 6 hours from flat to charge up on the mains, which I can vouch for, and that gives 6 hours playing time.

The charger/cigarette lighter adapter has written on it 9.5v; input 12v = 3a; output 9.5v = 2a. We've never tried to use the DVD player without the battery using the car charger, but it can be done off the mains. It's not a car specific DVD player, just the ordinary portable sort which occasionally finds its way into the Bongo if I remember to pack it before a long journey When we use it in the Bongo, we always use it on battery power only.

My biggest draw on the leisure battery is going to be my Webasto heater and whilst I don't understand the specs for that either the rated power consumption is 14-29 W. I know it takes a whack of charge when it starts up and then it happily hums away on a lower charge. The maximum time it can be run for is 2 hours, and at most I would normally use it for an hour before bed and probably an hour first thing when we wake up (although see below).

I'll have to speak to my husband about connecting an ammeter in series. I was totally crap at physics at school so that sort of thing is completely lost on me I could also sit down with my calculator and do some sums, but this weekend is a bit of an exception as we are likely to be using the DVD player more than usual and also the heater. It's not likely to be cold, but we are likely to be wet and I may heat up the Bongo just to try and dry some clothes off.

It's not an enormous issue, I just don't want to flatten my leisure battery and possibly wreck it (it is a 100aH Elecsol one, by the way). Unlikely in 2 and a half days, but if the weather is foul and we don't do our planned walking (the forecast is grim) my bored 4 year old son, and my friend's bored 4-tomorrow daughter and her 14 month old will be wanting to watch DVDs rather than follow the old fashioned pursuits of snakes & ladders and snap.

For anyone who's wondering why I'm going away at all with rain and 50 mph gusts of wind forecast, it's because my friend and her daughter both celebrate their birthdays this weekend and traditionally she has always camped on Dartmoor for her birthday with a group of friends. Now, if she can do it in a tent with two little children (and her husband), then I can definitely do it in the Bongo (with one child but no husband - he's working but mostly outside, so he hasn't got away with much by not joining us ).

[haydn callow]

If your battery is a 100ah as you say.
You will in fact never get 100 ah out of it.
Co's..
you will never get 100ah into it when you charge it...guess around 90ah.
Then when it discharges so it only has 40% charge left (around 40ah) it is very low and should be recharged.
90 - 40 will give you a useable supply of around 50ah...say 60ah tops.
I would work my sums out on that basis....60ah.
If you discharge your battery below this 40% level you could damage it and shorten it's life.
If you have a cheap multimeter (about £10 from most places) put it on the 20volt dc scale and measure across the battery terminals..
as a very rough guide (measure after the engine has been stopped a hour)
12.7 volts 90% battery available
12.5 70%
12.3 50%
12.0 40% further use could cause damage and shorten life.

these are very rough figures but you can get my drift.
Also if you really discharge the battery you may start blowing BIG fuses when you start your engine to recharge....

Best to give the battery a engine recharge before it drops to 12.0 volts.
Your alternator will provide 70/80 amps (never quite makes this rated output) so a hours running should put a good amount back in....measure the battery again after another hour and you will get a result.

(tickover charging really does not turn a alternator fast enough to provide a full output) I think alternators are ment to run at about 6000 RPM....(we used to put big flywheel pullys on our narrowboats to provide this speed) I don't suppose a Bongo pully gives more than twice engine revs so it is quite slow.(less than 2000 rpm at the alternator) = low output

[stilldesperate]

Some useful numbers on battery life there, Haydn, thanks.

Allison, If the charger can deliver (max) 9.5v at 2a, the wattage is 2 x 9.5 = 19 watts. As Romney (I think ) said, the current will, more than likely reduce, as the battery "fills up".

I'm not sure if measuring with an ammeter is worth the effort, as you are only getting a snapshot of the current taken when the DVD battery is at a particular state of discharge, and possibly dependant on the charge in the supplying (leisure) battery.

I was trying to reply to your post last night, but I was getting bogged down with the things that Romney explained so well!

SD

[mikeonb4c]

My biggest draw on the leisure battery is going to be my Webasto heater and whilst I don't understand the specs for that either the rated power consumption is 14-29 W. I know it takes a whack of charge when it starts up and then it happily hums away on a lower charge. The maximum time it can be run for is 2 hours, and at most I would normally use it for an hour before bed and probably an hour first thing when we wake up (although see below).

Are you talking about the Webasto heater (it reads as though you are)? That sounds really odd if so, as I thought the point of these things was so you could have them on for long periods (like all night) if need be in order to keep warm.

[Alison01326]

My biggest draw on the leisure battery is going to be my Webasto heater and whilst I don't understand the specs for that either the rated power consumption is 14-29 W. I know it takes a whack of charge when it starts up and then it happily hums away on a lower charge. The maximum time it can be run for is 2 hours, and at most I would normally use it for an hour before bed and probably an hour first thing when we wake up (although see below).

Are you talking about the Webasto heater (it reads as though you are)? That sounds really odd if so, as I thought the point of these things was so you could have them on for long periods (like all night) if need be in order to keep warm.

I am, Mike. Ours has a "countdown" timer on it. If we wanted it on all night, we would need to buy a bigger van!!! Even on its lowest setting, it pumps out a lot of heat. It may well be with the basic controls it can be on indefinitely, but we opted for one with a timer so that we could pre-set it to go on when we are out, or when we are asleep. One of the reasons we got it was to have a nice warm Bongo to get back into after outdoor activities. We haven't camped in sub-zero temperatures with it yet, but so far an hour before bed and an hour around when we get up has been more than adequate. I suspect if we did want it on for longer, we could pre-set the timer (there are three pre-sets) to kick in at two hourly intervals, and if we put it on manually beforehand we would get eight hours' heat.

Thank you all very much for your responses regarding leisure battery life and the DVD player issue. Will sit down and do some sums, and maybe buy a multimeter some time. Heading off shortly before the weather worsens and driving becomes a nightmare. We will only going 80 miles away but suspect I will have to take it pretty easy so likely to take more than a couple of hours to get there.